nomenclature - IUPAC name of a salt made of both cationic and anionic complexes

The IUPAC name of the complex compound [Ni(NH₃)₄][NiCl₄] is

In my opinion the correct answer should be Tetrachloronickel(II) tetraamminenickelate(II), because nickel has got more oxidation number when there are chlorine atoms and therefore it should be named first. But the correct answer seems to be Tetraamminenickel(II) tetrachloronickelate(II).

Answer

The coordination compound $\ce{[Ni(NH3)4][NiCl4]}$ contains two coordination entities, $\ce{[Ni(NH3)4]^2+}$ and $\ce{[NiCl4]^2-}$, which can be named separately.

The rules for formulating and naming coordination compounds are presented in Chapter IR-9 of the current version of Nomenclature of Inorganic Chemistry – IUPAC Recommendations 2005 (Red Book). An abridged version is included in the IUPAC Technical Report Brief guide to the nomenclature of inorganic chemistry. Pure Appl. Chem. 2015, 87(9–10), 1039–1049 as well as in the corresponding four-sided lift-out document, which is available as supplementary material.

Generally, ligand names are listed as prefixes to the name of the central atom along with any appropriate multipliers. Names of anionic coordination entities are furthermore given the ending ‘ate’. The oxidation number of the central atom may be indicated by a Roman numeral appended in parentheses to the central atom name; alternatively, the charge on the coordination entity may be indicated.

Therefore, the systematic name for $\ce{[Ni(NH3)4]^2+}$ is tetraamminenickel(II) or tetraamminenickel(2+), and the systematic name for $\ce{[NiCl4]^2-}$ is tetrachloridonickelate(II) or tetrachloridonickelate(2−).

In a salt made of both cationic and anionic coordination entities, the line formula for each ion is separately enclosed in square brackets. The cation is placed before the anion and no individual charges are shown:

$\ce{[Ni(NH3)4][NiCl4]}$

The systematic name of the entire compound is formed by combining the name of the electropositive constituent, cited first, with that of the electronegative constituent, both suitably qualified by any necessary multiplicative prefixes. The two parts of the name are separated by a space.

Therefore, the systematic name for $\ce{[Ni(NH3)4][NiCl4]}$ is tetraamminenickel(II) tetrachloridonickelate(II) or tetraamminenickel(2+) tetrachloridonickelate(2−).

Note that the ligand name ‘chloro’ is obsolete. According to current IUPAC recommendations, the correct ligand name is ‘chlorido’.